Rangefinders, based on measuring the time taken for a light pulse from a laser in a rangefinder to reach an object, the distance to which is to be measured, and return to the instrument after reflection by the object, are tested for correct function and precision using a known measuring distance. Testing can therefore only be carried out at places which are specially arranged for the purpose.
It is further known that a laser of the passive Q-switched laser type can transmit more than one light impulse when the laser excitation voltage is higher than normal. This is a drawback with this type of laser, since normally it is only desired to transmit one light pulse at each measuring occasion.